Video or image coding based on mapping of luma samples and scaling of chroma samples

Abstract

According to the disclosure of the present document, the granularity of value(s) of a chroma residual scaling factor can be controlled through explicit signaling of information on the value(s) of the chroma residual scaling factor. In addition, chroma residual scaling can be efficiently performed through implicit derivation of the information on the value(s) of the chroma residual scaling factor.

What is claimed is: 
     
       1. An image decoding method performed by a decoding apparatus, the image decoding method comprising:
 obtaining image information including luma mapping with chroma scaling (LMCS) related information, prediction related information, and residual information from a bitstream; 
 deriving LMCS codewords based on the LMCS related information; 
 determining an inter prediction mode as a prediction mode of a current block in a current picture based on the prediction related information; 
 generating prediction chroma samples for the current block based on the prediction mode; 
 deriving transform coefficients for the current block based on the residual information; 
 generating residual chroma samples for the current block based on the transform coefficients; 
 deriving a chroma residual scaling factor for luma dependent chroma residual scaling based on the LMCS codewords and luma samples; and 
 generating reconstructed chroma samples for the current block based on the chroma residual scaling factor, 
 wherein the LMCS related information includes information on bins and information on the LMCS codewords, 
 wherein a minimum bin index and a maximum bin index are derived based on the information on the bins, 
 wherein the LMCS codewords are derived based on the information on the LMCS codewords, 
 wherein the image information includes information on an absolute value of a chroma residual scaling delta value and information on a sign of the chroma residual scaling delta value, and 
 wherein the chroma residual scaling factor is derived based on the LMCS codewords, the information on the absolute value of the chroma residual scaling delta value and the information on the sign of the chroma residual scaling delta value. 
 
     
     
       2. An image encoding method performed by an encoding apparatus, the image encoding method comprising:
 deriving luma mapping with chroma scaling (LMCS) codewords; 
 generating LMCS related information based on the LMCS codewords; 
 determining an inter prediction mode as a prediction mode of a current block in a current picture; 
 generating prediction related information based on the prediction mode; 
 generating prediction chroma samples for the current block based on the prediction mode; 
 generating residual chroma samples for the current block based on the prediction chroma samples; 
 deriving a chroma residual scaling factor for luma dependent chroma residual scaling based on the LMCS codewords and luma samples; 
 generating scaled residual chroma samples for the current block based on the chroma residual scaling factor; 
 deriving transform coefficients for the current block based on the scaled residual chroma samples; 
 generating residual information based on the transform coefficients; and 
 encoding image information including the LMCS related information, the prediction related information, and the residual information, 
 wherein the LMCS related information includes information on bins and information on the LMCS codewords, 
 wherein the information on bins represents a minimum bin index and a maximum bin index, 
 wherein the information on the LMCS codewords represents the LMCS codewords, 
 wherein the image information includes information on an absolute value of a chroma residual scaling delta value and information on a sign of the chroma residual scaling delta value, and 
 wherein the LMCS codewords, the information on the absolute value of the chroma residual scaling delta value and the information on the sign of the chroma residual scaling delta value represent the chroma residual scaling factor. 
 
     
     
       3. A transmission method of data for an image, the transmission method comprising:
 obtaining a bitstream of the image, wherein the bitstream is generated based on deriving luma mapping with chroma scaling (LMCS) codewords, generating LMCS related information based on the LMCS codewords, determining an inter prediction mode as a prediction mode of a current block in a current picture, generating prediction related information based on the prediction mode, generating prediction chroma samples based on the prediction mode, generating residual chroma samples based on the prediction chroma samples, deriving a chroma residual scaling factor for luma dependent chroma residual scaling based on the LMCS codewords and luma samples, generating scaled residual chroma samples based on the chroma residual scaling factor, deriving transform coefficients based on the scaled residual chroma samples, generating residual information based on the transform coefficients, and encoding image information including the LMCS related information, the prediction related information and the residual information; and 
 transmitting the data comprising the bitstream, 
 wherein the LMCS related information includes information on bins and information on the LMCS codewords, 
 wherein the information on bins represents a minimum bin index and a maximum bin index, 
 wherein the information on the LMCS codewords represents the LMCS codewords, 
 wherein the image information includes information on an absolute value of a chroma residual scaling delta value and information on a sign of the chroma residual scaling delta value, and 
 wherein the LMCS codewords, the information on the absolute value of the chroma residual scaling delta value and the information on the sign of the chroma residual scaling delta value represent the chroma residual scaling factor.